1. Field of the Invention
The present invention relates, in general, to an image sensor and, more particularly, to an image sensor capable of judging proximity to a subject, in which the distance to a subject is judged based on a change in output voltage value by the presence or absence of a specific band of wavelengths of infrared (IR) when measured by optical sensors such as proximity pixels, thereby enabling an ordinary image sensor to easily realize a proximity function, and making it possible to minimize damage to a quality of image when the image is picked up in a night photography mode or in a proximity photography mode.
2. Description of the Related Art
Generally, image sensors using a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) has an absorption band between 400 nm and 1100 nm. Further, the visible light usually has a wavelength ranging from 380 nm to 650 nm, and the infrared (IR) light has a wavelength ranging from 650 nm to 1100 nm. These image sensors usually employ an IR cutoff filter, which transmits light having a wavelength of 650 nm or less and cuts off light having a wavelength of 650 nm or more, i.e. an IR band of wavelengths, so as to be able to sense and display the same colors as colors which are visible to human eye.
In order to photograph a closed space, etc. using this image sensor in an environment where external light is weak, for instance at night or after a lamp is turned off, as in a surveillance camera and obtain an image, use was generally made of an IR region of light as the light of a light source. In this manner, when the IR region of light is used as the light of the light source according to an external environment, the IR region of light is cut off by the IR cutoff filter if the light from an external light source is sufficient, so that a quality of image is improved. However, when the light from the external light source is insufficient to use the IR region of light as the light of the light source, the IR region of light is allowed to reach the image sensor by removing the IR cutoff filter.
Thus, a conventional system using the image sensor should be provided with moving means capable of varying a position of the IR cutoff filter according to the external light source. In this manner, because the moving means for mechanically moving the IR cutoff filter is installed, the surveillance camera, etc. become bulky, and production cost is increased.
Further, an IR light emitting diode (LED) used in the conventional image sensor is generally limited only to a function as a light source for obtaining an image in a dark environment.
Recently, in using mobile instruments such as digital cameras or mobile phones, electronic instruments, and so on, there is increasing a demand for a proximity function in which it is determined how much a user is separated from the mobile instrument, and the mobile instrument is allowed to be automatically controlled. As such, there is a proposal to use the mobile instrument in such a manner that, in the case where a distance between the user and the mobile instrument is measured, and thus the user is determined to be adjacent to the mobile instrument on the basis of information on the distance, the mobile instrument can automatically interrupt supply of power to a back light unit (BLU) to reduce consumption of the power, or automatically stop operation of a touch sensor to prevent malfunction.
Conventionally, in order to realize this proximity function, a proximity sensor separately manufactured using an LED and a photodetector is generally installed on the mobile instrument or the electronic instrument.
However, in the case where the separate proximity sensor is installed in this way, the volume of the mobile instrument or the electronic instrument increases to go against a current technical trend toward possibility of miniaturizing products and realizing multiple functions. In addition, the production cost for installing the separate proximity sensor is increased.